In order to be usable in space, linear accelerators that utilize a radio-frequency quadrupole (RFQ) must be able to withstand the forces encountered during a rocket launch. In addition, it is desirable that RFQ accelerators be lightweight, easily fabricated, and easily adjusted for either space or ground applications and, more particularly, portable ground systems. Existing RFQ accelerators have failed to accomplish these goals and, thus, are unacceptable for these applications.
One of the major disadvantages of current RFQ accelerators is that they are constructed of very precisely made parts that are imprecisely mounted inside of an accelerator shell. Complex adjustment mechanisms are required to align the vane tips of the RFQ accelerator in the precise spatial relationship that is critical to achieving uniform field distributions in the four quadrants of the RFQ accelerator. Precision alignment is attained by repeated testing and readjustment of the position of the RFQ vane tips. This trial and error method is time consuming and difficult.
Another disadvantage of present RFQ accelerators is that prior adjustment mechanisms have usually relied on independently tensioning each of the four vanes and the resonator shell. During the alignment process, the tension developed in adjusting one vane causes distortion in the shape of the resonator shell and consequent misalignment of the other vanes. As a result, alignment is crude and imprecise. Consequently, maximum performance of the RFQ accelerator is difficult to achieve. Furthermore, because the adjustment mechanisms are under constant tension, they are inherently unstable and can easily go out of adjustment when vibrated.
In addition to alignment, the four RFQ vanes must be attached longitudinally along the RFQ resonator shell to have a good radio-frequency current contact for conducting the large currents necessary to excite the vane tips. Previously developed RFQ accelerators use either flexible welded joints or adjustment mechanisms with built-in contacts. These earlier configurations have the disadvantage of requiring two contact joints per vane, for a total of eight per RFQ accelerator, to permit adjustment of the vane in several directions while maintaining current contact. These additional contacts decrease the efficiency while increasing the weight, complexity, and cost of previous RFQ accelerators. Further, the current contact joints do not maintain contact when subjected to severe vibrational loads.